First of all, you will need to install an ssh server on your VM before you can ssh to it. You will probably need to do this with a VNC Viewer. When your in your VM, you can install OpenSSH with:
apt-get install openssh-server
Make sure your VM is powered on before proceeding. If you want to access your VM from another Redbrick server, you can ignore the login details (passwords, etc.) on the page that comes up after you turn on the VM. If you're logging in from an external computer, take note of those details and follow the instructions below - and/or on that page - carefully.
Access from other Redbrick servers
Note your VM's IP address from the VM Management page (not from the page that comes up after you switch on your VM). To login simply ssh to that IP address, with your VM user/pass (not your Redbrick login details). You will have set up these details when installing the operating system on your VM.
Note that this is the method to use once you login to Redbrick using PuTTy or whatever, as once you're logged in, you're using Redbrick servers.
Access from an external machine
You will need to setup a tunnel to get to your VM, if you're accessing from outside Redbrick. To do this, type:
ssh -L 1337:YOUR_VM_IP_ADDRESS:22 firstname.lastname@example.org
This binds port 1337 on your own computer to your VM (on port 22, the ssh service). So to connect to your VM:
ssh 127.0.0.1 -p 1337
This is the method to use when you're not logged directly onto Redbrick, such as when you're using your home Linux machine.